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Abstract

Purpose: To examine the effect of prolonged cycling on ratings of perceived exertion (RPE) in boys and men and whether carbohydrate (CHO) ingestion would lower RPE during exercise.

Methods: Ten boys (9–10 yr) and 10 men (20–25 yr) cycled for 60 min at ∼70% V̇O2peak on two occasions. In a double-blind, counterbalanced design, a total volume of 24 mL·kg−1 body mass of either a 6% CHO-electrolyte (CT) or flavored water (WT) beverage was consumed intermittently before and during exercise in each trial. Oxygen consumption (V̇O2), ventilation (V̇E), respiratory rate (RR), RPE (Borg’s 6–20 scale), and heart rate (HR) were recorded periodically throughout exercise. Plasma glucose (GLU) was determined before and after exercise.

Results: Postexercise GLU was not different between age groups but higher (P < 0.001) during CT (5.6 ± 0.2 mmol·L−1) compared with WT (4.7 ± 0.1 mmol·L−1). CHO ingestion had no effect (P > 0.05) on V̇O2, V̇E, RR, or RPE in either group. RR during exercise was higher (P < 0.01) in boys (39.0 ± 2.2 breaths·min−1) than in men (30.9 ± 1.3 breaths·min−1). HR was slightly higher (P = 0.047) during CT (160 ± 3 beats·min−1) compared with WT (156 ± 4 beats·min−1) and increased less over time (P < 0.01) in boys compared with men. RPE at 5 min of exercise was similar (P > 0.05) between boys (11.8 ± 0.7) and men (12.0 ± 0.7) but increased faster (P < 0.01) over time in boys. The average exercise RPE was higher (P < 0.01) in boys (15.8 ± 0.5) than in men (14.0 ± 0.4).

Conclusions: The higher and faster increase in RPE during exercise in boys, compared with men, may reflect a sensitivity to RR that outweighed any effect of CHO ingestion on RPE.

The rating of perceived exertion (RPE) during exercise is a subjective indication of physiological cues, such as respiratory-metabolic (e.g., ventilatory drive) or peripheral (e.g., lactate accumulation) and psychological cues (e.g., cognitive style) arising from the activity (20). Borg’s 6–20 RPE scale, constructed to integrate the respiratory-metabolic and peripheral signals of physical strain (4), has been employed extensively in the adult literature with relatively fewer applications to the pediatric population (20). Although child-oriented scales have been developed to study perceptual responses to exercise in children (24,30), Borg’s 15-grade scale is considered to be both valid and reliable for use with children as young as 9 yr old (2,13,16).

Compared with adults, children tend to assign a lower (2) or similar (14) RPE to the same relative exercise intensity. It has also been shown (2) that the ratio of RPE to heart rate (HR) tends to be lower in children than in adults, suggesting that for a given physiological strain, children rate exercise to be lighter. However, the majority of studies conducted with children, regardless of the effort scale used, have adopted only short-duration (e.g., ≤20 min) exercise of varying intensity (13). Consequently, there is a clear lack of research comparing RPE over a prolonged period of constant-load exercise between children and adults. Recently, Cheatham et al. (7) found that RPE (Borg’s 6–20 scale) increased faster over 40 min of cycling exercise at the same relative intensity in 10- to 13-yr-old boys compared with 18- to 25-yr-old men. These authors suggested that the boys may not have been accustomed to the exercise employed and, therefore, experienced a greater degree of muscle fatigue reflected by a faster increase in RPE.

The relationship between fatigue and RPE has been studied, at least in adults, from an energy perspective. It is well known that the onset of fatigue can be delayed by ingesting carbohydrate (CHO) throughout exercise (8). In adults, the consumption of CHO, compared with water, can also lower RPE during cycling exercise (6,9,26,29). However, the benefit of CHO ingestion seems to become apparent only after ∼60 min of exercise, and although the mechanisms for this effect are not clear, they may be related to maintained levels of plasma glucose (9,19) and higher oxidation rates of the ingested CHO (6,25). We have also shown that glucose ingestion (∼1.4 g·kg−1 body weight) before and during 60 min of cycling at ∼60% V̇O2peak lowered RPE in healthy 13- to 19-yr-old adolescent boys but not in adolescent boys with insulin-dependent diabetes mellitus (22). In contrast, we have also reported that CHO ingestion (∼0.8 g·kg−1 body weight) had no effect on RPE during 50 min of intermittent exercise at ∼50% V̇O2peak in a warm environment (34–35°C, 42–45% relative humidity) in healthy 9- to 12-yr-old children (18). The different exercise intensities, environmental conditions, rate of CHO ingestion, and age of the subjects in our previous studies may explain these conflicting results. To our knowledge, no study has compared the effect of CHO ingestion on RPE in children and adults under identical experimental conditions.

Therefore, the purpose of this study was to examine the effects of prolonged (i.e., 60 min) exercise and CHO ingestion on RPE in a group of 9- and 10-yr-old boys and a group of 20- to 25-yr-old men. We hypothesized that, during exercise, RPE would increase faster in the boys compared with the men, and that CHO ingestion would lower RPE in the boys but not in the men. We hypothesized that CHO ingestion would have no effect on RPE in the men because exercise duration was restricted to 60 min.

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